The present disclosure relates to a focus servo process automatic selecting method for automatically selecting one of astigmatism detection (AD) and differential astigmatism detection (DAD) before a focus-on operation of an optical pickup apparatus to realize an optimum focus servo.
A recent optical pickup device of a disk driver detects various storing media such as digital versatile disk (DVD)±recording (R), DVD±rewritable (RW), DVD±R double layer (DL), and DVD random access memory (RAM) to play the medium. An optical pickup device of a DVD system can play disks having different thicknesses, track pitches, and data densities using one photodetector. Also, the optical pickup device performs an operation of determining the kind of an inserted disk upon insertion of the disk. This operation is simultaneously performed with a focus servo operation of condensing a beam on a disk surface. Generally, the optical pickup device determines the kinds of various disks using a time difference between a time at which a signal is reflected by a data surface of a DVD, and a time at which the signal reflected by the surface of the DVD is incident.
Currently, most of optical pickup focus control is performed using AD with respect to a DVD±R disk, an RW disk, and an R DL disk, and is performed using DAD with respect to a DVD RAM disk.